Hyrogenation of unsaturated compounds

ABSTRACT

The invention described in the specification concerns a process for the homogeneous liquid phase hydrogenation of an olefinically or acetylenically unsaturated organic compound to produce a compound having a lower degree of unsaturation by contact of the said organic compound with molecular hydrogen in the presence of a catalyst solution containing a catalytically effective amount of a cation selected from the group consisting of: 
     
         M.sup.n.sup.+.sub.2 ; M.sub.2 (OCOR).sup.n.sup.+.sub.4.sup.-n ; M.sub.2 
    
      (OCSR) n   +   4   -n  and M 2  (SCSR) n   +   4   -n   
     The said solution being prepared by the addition of strong acid to a solution of a compound selected from the group consisting of: 
     
         M.sub.2 (OCOR).sub.4 ; M.sub.2 (OCOR).sub.4 L; M.sub.2 (OCOR).sub.4 L.sub.2 
    
      ; M 2  (OCSR) 4  ; M 2  (OCSR) 4  L; 
     
         M.sub.2 (OCSR).sub.4 L.sub.2 ; M.sub.2 (SCSR).sub.4 ; M.sub.2 (SCSR).sub.4 
    
      L 
     and 
     
         M.sub.2 (SCSR).sub.4 L.sub.2 
    
     where M is a metal selected from the group consisting of Mo, Cr, Cu, Re and metals of the platinum group; 
     R is selected from the group consisting of alkyl and aryl; 
     L is ligand selected from the group consisting of H 2  O, CH 3  OH, C 2  H 5  OH, CO, pyridine, Cl -and  Br -;   
     n is a positive integer from 1 to 4; 
     (OCOR) represents a carboxylate radical; 
     (OCSR) represents a thiocarboxylate radical, and 
     (SCSR) represents a dithiocarboxylate radical, and the said solution including a stabilising amount of a donor ligand selected from the group consisting of pyridine, quinoline, dimethylaniline, dibutyl sulphide, dimethyl sulphide, triphenyl phosphine oxide, phenyl isocyanide, acetonitrile, phosphorus tri-isocyanate, phosphorus tri-isothiocyanate, stannous halide, germanium (II) halide and a ligand having the formula MR&#39; 3  where M is selected from the group consisting of phosphorus, arsenic and antimony and R&#39; is selected from the group consisting of alkyl, aryl and aryloxy radicals.

This application is a continuation-in-part of Ser. No. 53031 filed July7, 1970, now issued as U.S. Pat. No. 3,725,305. Said patent describesand claims catalyst compositions containing a catalytically effectiveamount of a cation selected from the group consisting of:

M₂ ^(n) ⁺

M₂ (ocor)₄ _(-n) ^(n) ⁺

M₂ (ocsr)₄ _(-n) ^(n) ⁺

And

M₂ (scsr)₄ _(-n) ^(n) ⁺

Where M is a metal selected from the group consisting of Mo, Cr, Cu, Reand metals of the platinum group;

R is selected from the group consisting of alkyl and aryl;

N is a positive integer from 1 to 4

(OCOR) represents a carboxylate radical;

(OCSR) represents a thiocarboxylate radical, and

(SCSR) represents a dithiocarboxylate radical.

According to one aspect of the present invention there is provided aprocess for the homogeneous liquid phase hydrogenation of anolefinically or acetylenically unsaturated organic compound to produce acompound having a lower degree of unsaturation by contact of the saidorganic compound with molecular hydrogen in the presence of a catalystsolution containing a catalytically effective amount of a cationselected from the group consisting of:

M₂ ^(n) ⁺

M₂ (ocor)₄ _(-n) ^(n) ⁺

M₂ (ocsr)₄ _(-n) ^(n) ⁺

and

M₂ (scsr)₄ _(-n) ^(n) ⁺

the said solution being prepared by the addition of strong acid to asolution of a compound selected from the group consisting of

M₂ (ocor)₄

m₂ (ocor)₄ l

m₂ (ocor)₄ l₂

m₂ (ocsr)₄

m₂ (ocsr)₄ l

m₂ (ocsr)₄ l₂

m₂ (scsr)₄

m₂ (scsr)₄ l

and

M₂ (scsr)₄ l₂

where M is a metal selected from the group consisting of Mo, Cr, Cu, Reand metals of the platinum group;

R is selected from the group consisting of alkyl and aryl;

L is a ligand selected from the group consisting of

H₂ o, ch₃ oh, c₂ h₅ oh, co, pyridine, Cl⁻ and Br^(-;)

n is a positive integer from 1 to 4;

(OCOR) represents a carboxylate radical;

(OCSR) represents a thiocarboxylate radical, and

(SCSR) represents a dithiocarboxylate radical, and the said solutionincluding a stabilising amount of a donor ligand selected from the groupconsisting of pyridine, quinoline, dimethylaniline, dibutyl sulphide,dimethyl sulphoxide, triphenyl phosphine oxide, phenyl isocyanide,acetonitrile, phosphorus tri-isocyanate, phosphorus tri-isothiocyanate,stannous halide, germanium (II) halide and a ligand having the formulaMR₃ ' where M is selected from the group consisting of phosphorus,arsenic and antimony and R' is selected from the group consisting ofalkyl, aryl and aryloxy radicals.

The cationic species produced are generally, but not necessarilybinuclear. When the oxidation state of the metal is formally II abinuclear metallic cation may have a charge of +4. In one example, thereaction proceeds as follows:

    Rh.sub.2 (OCOCH.sub.3).sub.4 + 4H.sup.+ → Rh.sub.2.sup.4.sup.+  + 4CH.sub.3 COOH

Partial displacement of the carboxylate or substituted carboxylate,instead of full displacement may take place; for example:

    Rh.sub.2 (OCOCH.sub.3).sub.4 + H.sup.+ → Rh.sub.2 (OCOOH.sub.3).sub.3.sup.+  + CH.sub.3 COOH

In this case the cationic species with one positive charge also showsgood catalytic activity.

Some examples of the catalyst precursor compounds which produce activespecies according to this invention on protonation are:

    Rh.sub.2 (OCOR).sub.4                                                                      Rh.sub.2 (OCSR).sub.4                                                                       Rh.sub.2 (SCSR).sub.4                              Mo.sub.2 (OCOR).sub.4                                                                      Mo.sub.2 (OCSR).sub.4                                                                       Mo.sub.2 (SCSR).sub.4 -Cr.sub.2 (OCOR).sub.4                                  Cr.sub.2 (OCSR).sub.4  Cr.sub.2 (SCSR).sub.4       Ru.sub.2 (OCOR).sub.4 Cl                                                                   Ru.sub.2 (OCSR).sub.4 Cl                                                                    Ru.sub.2 (SCSR).sub.4 Cl                           Ru.sub.2 (OCOR).sub.4                                                                      Ru.sub.2 (OCSR).sub.4                                                                       Ru.sub.2 (SCSR).sub.4                              Cu.sub.2 (OCOR).sub.4                                                                      Cu.sub.2 (OCSR).sub.4                                                                       Cu.sub.2 (SCSR).sub.4                              Re.sub.2 (OCOR).sub.4 Cl.sub.2                                                             Re.sub.2 (OCSR).sub.4 Cl.sub.2                                                              Re.sub.2 (SCSR).sub.4 Cl.sub.2                     Re.sub.2 (OCOR).sub.4 (CO).sub.2                                                           Re.sub.2 (OCSR).sub.4 (CO).sub.2                                                            Re.sub.2 (SCSR).sub.4 (CO).sub.2                   Re.sub.2 (OCOR).sub.4                                                                      Re.sub.2 (OCSR).sub.4                                                                       Re.sub.2 (SCSR).sub.4                              Ir.sub.2 (OCOR).sub.4                                                                      Ir.sub.2 (OCSR).sub.4                                                                       Ir.sub.2 (SCSR).sub.4                          

Especially effective are the tetracetate compounds, i.e. those of thefirst column, when R = CH₃.

Oxidation states other than 2 can be involved. For example the rutheniumcomplex Ru₂ (OCOR)₄ Cl contains formally Ru(II) and Ru(III) (see example3 below). The rhenium complex Re₂ (OCOR)₄ Cl₂ contains formally,Re(III).

The strong acid referred to above may, for example, be fluoroboric acid,perchloric acid, fluorosulphuric acid, trifluoromethane sulphuric acid,sulphuric acid or hydrofluoric acid; hydrofluoric acid may be used aloneor in combination with a Lewis acid such as SbF₅, SiF₄ or BF₃.

As mentioned in the parent application the catalyst composition containsthe species:

M₂ ^(n) ⁺ ;

M₂ (ocor)₄ _(-n) ^(n) ⁺ ;

M₂ (ocsr)₄ _(-n) ^(n) ⁺,

or

M₂ (scsr)₄ _(-n) ^(n) ⁺,

and

for the purpose of brevity and clarity, additional neutral or negativeligands indicated above, such as H₂ O, are not always indicated as beingpresent in cationic species in this specification. This would not, ofcourse, be taken to mean that such species are definitely excluded.

The cationic species may be exchanged on to cation exchange resins orsimilar exchange solids such as zeolites, phosphates such as sodiumhexametaphosphate, i.e. "Calgon" etc. They may also be adsorbed on toactivated charcoal and other similar solids.

The solid material is preferably a cation exchange resin such assulphonated polystyrene in the form of porous resin beads.

If, when carrying out the invention, the cationic species liberated byprotonation is adsorbed on to a cation exchange resin (or a similarexchange material as described above), the resulting material is useful,for example, as a heterogeneous catalyst for hydrogenation,carbonylation, hydroformylation and the related reactions of olefine orother organic materials either in the gas or liquid phase, or insuspension solution (with beads of ion-exchange resin, for example).Ambient or elevated temperatures may be used.

Such solid state catalysts will also promote for example:

a. the carbonylation of methanol to acetic acid,

b. the carbonylation of amines to amides,

c. the isomerisation and disproportionation of alkenes, alkapolyenes andrelated compounds,

and

d. the hydrosilation of alkenes.

Solutions of the metal carboxylate, thio or dithiocarboxylate inmethanol (or a similarly polar solvent) in the presence of excessprotonating acid (e.g. HBF₄) and subsequent addition of additional donorligand for stabilisation purposes are active catalysts for example forthe hydrogenation of alkenes of all types including conjugated polyenes,acetylenes generally (R'C .tbd. CR where R and R' may also be H) andother unsaturated substrates containing carbon -- carbon double andtriple bonds such as carboxylic acids, ketones, ethers, steroids, estersand alcohols, for example at 25°C and atmospheric pressure.

Some suitable donor ligands for stabilisation purposes are:

R₁ r₂ r₃ p

r₁ r₂ r₃ as

R₁ r₂ r₃ sb

R₁ r₂ s

r₁ r₂ r₃ n

in which R₁, R₂ and R₃ may be the same or different and may be hydrogen,aryl or alkyl substituents. Heterocyclic N-bases such as pyridine,dipyridyl, etc. are also suitable donor ligands.

Suitable organo-phosphorus, organo-arsenic and organo-antimony ligandswhich may comprise part of this invention are those consisting oftertiary organo-phosphorus, organo-arsenic, and organo-antimonycompounds in which the phosphorus, arsenic, and antimony atoms aretrivalent and are referred to in this specification as phosphines,arsines and stibines, respectively. In the group of suitable ligandscontaining the trivalent phosphorus, arsenic, and antimony atomsemployed in the catalyst of this invention, the individual phosphorus,arsenic, and antimony atom has one available or unshared pair ofelectrons. An aryl or aryloxy derivative of trivalent phosphorus,arsenic, and antimony with the foregoing electronic configuration is,therefore, a suitable ligand for the catalyst of this invention. Suchradicals, therefore, are bonded to the phosphorus, arsenic, and antimonyatoms, and the radicals are selected from the group consisting of aryland aryloxy groups. However, the preferred phosphine, arsine, andstibine ligands are those consisting of at least one, but preferablythree aryl-and/or aryloxy-groups as the organic moieties. For example,preferred ligands are illustrated by the following structural formulaand examples:

Mr₃ ' where M is P, As, Sb, and R' = phenyl(C₆ H₅ --), phenoxy (C₆ H₅O--) toly [CH₃ (C₆ H₄) --], xylyl (CH₃ C₆ H₃ CH₃) e.g. P(C₆ H₅)₃ P(C₆ H₅O).sub. 3, As(C₆ H₅)₃, Sb(C₆ H₅)₃, P[CH₃ (C₆ H₄)]₃. However, a morepreferred group of ligands includes the triphenylphosphines,triphenylphosphites, triphenylarsines and triphenylarsenites. Theimportant component is the aryl or aryloxy group, e.g. the phenyl orphenoxy radical. However, the molecule may also contain some aryl groupsin addition to the aryloxy radical.

A preferred group of ligands associated with the organic phosphorus,arsenic, and antimony derivatives has aryl and aryloxy radicals havingfrom 6 to 18 carbon atoms.

Generally speaking, suitable donor ligands for stabilisation purposesare:

a. an organic isocyanide;

b. an organic compound having in the molecule an atom of an elementselected from groups 5B or 6B of the Periodic Table, that is, usually aN, P, As, Sb, O, S or Se atom, such atom being in such a valency statethat it possesses a lone pair of electrons, or

c. a stannous or germanium (II) halide.

Preferred ligands within the definition of categories (a) and (b)include: tertiary amines, phosphines, arsines and stibines; organicnitriles and isocyanides; sulphoxides, phosphine oxides, dialkylsulphides and mercaptans.

For example, there may be employed pyridine, quinoline ordimethylaniline; though less basic compounds are preferred, for example,tributyl or triphenyl phosphine, trimethyl phosphite, ethyl diphenylphosphine, dimethylphenyl arsine, triphenyl arsine or stibine, dibutylsulphide, dimethyl sulphoxide, triphenyl phosphine oxide, phenylisocyanide or acetonitrile. Also to be treated as organic compounds forpresent purposes are ligands within category (b) such as phosphorustri-isocyanate and phosphorus tri-isothio cyanate.

Such donor ligands for stabilisation purposes are often described asbiphyllic ligands. By "biphyllic ligand" is meant a compound having anelement with a pair of electrons capable of forming a co-ordinate bondwith a metal atom and simultaneously having the ability to acceptelectrons from the metal, thereby providing additional stability to theresulting complex. The term biphyllic ligand has been defined by R. G.Pearson -- see J.A.C.S. 82 787 (1960). The carbon monoxide molecule isan example of a suitable biphyllic ligand. The biphyllic ligand may alsobe a polydentate compound, co-ordinating at more than one position tothe central metal atom or ion.

Catalysts according to this invention have an advantage over otherhomogeneous catalysts such as RhCl(PPh₃)₃, RhH(CO)(P Ph₃)₃ or RuH(Cl) (PPh₃)₃ in that they are completely and readily soluble in polar solventssuch as methanol, olefinic substrates to be hydrogenated which areinsoluble or sparingly soluble or benzene-alcohol mixtures can now behydrogenated in a wholly polar medium.

Catalyst solutions according to this invention will also catalyse thehydroformylation reactions of alkenes, alkynes and other unsaturatedmaterials with C=C and C.tbd.C bonds. These reactions may be carried outusing carbon monoxide and hydrogen mixtures (which can be 1:1 or otherratios) at temperatures from 15° - 200°C or above, and at pressures from1 atm upwards.

Catalyst solutions according to this invention will also isomerisealkenes and other unsaturated substances by causing double bondmigration as well as cis ⃡ trans isomerisation.

Solutions according to this invention will catalyse the formation ofacetic acid from methanol and carbon monoxide under mild conditions(e.g. 100°C and under 50 atm. pressure). In this case the presence of ahalogen promoter is desirable and methyl iodide has been found to be asatisfactory one in this case.

The foregoing are only some of the chemical reactions for which thecompositions according to the invention can act as catalysts.

The invention will now be described in more detail with reference to thefollowing examples.

EXAMPLE 1

Commercial rhodium trichloride trihydrate (5.0 g) and sodium acetatetrihydrate (10.0 g) in glacial acetic acid (100 ml) and absolute ethanol(100 ml) were gently refluxed under nitrogen for an hour.

The initial red solution rapidly became green and a green solid wasdeposited. After cooling to room temperature the green solid wascollected by filtration through a Buchner or sintered filter funnel.

The crude product was dissolved in boiling methanol (ca. 600 ml) andfiltered; after concentration to about 400 ml the solution was kept in arefrigerator overnight. After collection of the crystals, the solutionwas concentrated and cooled to yield a further small amount of themethanol adduct [Rh(OCOCH₃)₂ ]₂.2CH₃ OH.

The blue green adduct was heated in vacuum at 45° for 20 hours to yieldemerald green crystals of [Rh(OCOCH₃)₂ ]₂. A check on the removal ofmethanol was made periodically by taking an infrared spectrum.

Properties

The copper acetate type structure has been shown by X-ray diffraction.The complex is diamagnetic; it is only slightly soluble in water,methanol, acetone, etc., giving green solutions. Adducts with a varietyof ligands have been characterised.

The infrared spectrum has bands at 1580s, 1425s, 1355m in nujol mulls(in hexachlorobutadiene 1445s, 1415s, 1350m) due to carboxylatefrequencies, as well as CH₃ absorption.

The addition of a stoichiometric amount of aqueous concentratedfluoroboric acid to a methanol or water suspension of the acetate of 60°gives a clear green solution after about 12 hours which contains the ionRh₂ ⁴ ⁺.

The green solution of Rh₂ ⁴ ⁺ in methanol normally requires the presenceof other stabilising donor ligands, as described above in order toexhibit any substantial catalytic activity.

On the addition of a stabilising donor ligand such as triphenylphosphine, for example, to the green solution an active catalyst for thehomogeneous hydrogenation of alkenes and alkynes is obtained.Comparative rates of reaction under standard conditions are given inExample 2.

The catalyst solution in the following examples was made up as requiredfrom a stock solution of Rh₂ ⁴ ⁺ in methanol and the phosphine wasadded, via a syringe, to the reaction flask. The apparatus and generaltechniques used have been described previously in J. Chem. Soc. (A) 1966p.1711.

Catalytic activity of the protonated solution is highest with a Rh : PPh₃ ratio of 1:2. The activity appears to be poisoned by oxygen andcarbon monoxide, and this effect cannot be reversed by sweeping withhydrogen.

The solutions with Rh:P Ph₃ of 1:2 are normally red, but on addition ofcertain unsaturated substances, notably unsaturated carboxylic acids andalcohols, a change in colour to yellow-green occurs, presumably due tothe formation of complexes, possibly of Rh (II).

The methanolic solutions of Rh₂ ⁴ ⁺ react with many donor ligands, e.g.R₂ NCS₂ ⁻, amines, etc., to give a wide variety of complexes. Withoxygen donors such as dimethyl sulphoxide, hexamethyl phosphoramide,alcohols, ketones and esters, the solutions stay green and presumablythese substances are merely solvating the ion.

Where the preparation of a carboxylate compound complex or ionic speciesis described in this specification, the corresponding thio- anddithio-analogues may be assumed to be prepared similarly, withappropriate modifications.

EXAMPLE 2

Rhodium system

The activity of protonated Rh solution prepared as in Example 1 for thehydrogenation of various substrates is given below:

( [Rh] = 2.50 mM, [acetylene or olefin] = 1.0 M, P'_(H).sbsb.2 = 45 cm,solvent : methanol,

Reaction temperature 25°, [PPh₃ ] = 5.0 mM)

    Substrate  Rate ml/min                                                                              Substrate   Rate ml/min                                 ______________________________________                                        Hex-1-ene  10.9       n-Hex-1-yne 34.2                                        cis and trans                                                                            3.3        3 methyl butyn                                          HeX-2-ene             1-ol-3      44.8                                        cis Hept-2-ene                                                                           2.2        Propargyl                                                                     alcohol     17.6.sup.a                                  Cyclohexene                                                                              1.1        Acetylene                                                                     dicarboxylic                                                                  acid        <0.1.sup.a                                  1,5 Hexadiene                                                                            36.6                                                               Allyphenyl ether                                                                         14.1       Cyclo octa-                                                                   1,5 diene   0.6.sup.b                                   Diethyl maleate                                                                          4.8                                                                Maleic acid                                                                              0.2                                                                ______________________________________                                         .sup.a [PPh.sub.3 ] = 20.0 mM                                                 .sup.b P.sub.H .sbsb.2  = 30 mm                                          

EXAMPLE 3

Ruthenium system

The activity of protonated Ru₂ (OCOCH₃)₄ Cl for the hydrogenation ofvarious substrates is given below:

( [Ru] = 2.50 mM, [acetylene or olefin] = 1.0.M, P'_(H).sbsb.2 = 45 cm,solvent or methanol

Reaction temperature 25°, [PPh₃ ] = 5.0 mM)

    Substrate   Rate ml/min                                                                              Substrate  Rate ml/min                                 ______________________________________                                        Hex-1-ene   30.5       3 methyl but-                                                                 1-yne-3-ol 14.1                                        cis,trans Hex-                                                                            0.5                                                               2-ene                                                                         1,5 Hexadiene                                                                             46.2                                                              Allyl phenyl ether                                                                        1.3 *                                                             ______________________________________                                         * P'.sub.H .sbsb.2  = 50 cm.                                             

EXAMPLE 3A

The activity of a ruthenium catalyst made by the protonation of Ru₂(OCOMe)₄.2PPH₃ under hydrogen is given below:

( [Ru] = 2.50 mM, [acetylene or olefin] = 1.0M, P_(H).sbsb.2 = 45 cm,reaction temperature = 30°C, PPh₃ = 5.0 mM, solvent = methanol

    Substrate     Rate ml/min                                                     ______________________________________                                        Hex-1-yne     0.4.sup.a                                                       Hex-1-ene     41.8                                                            Cyclo octa -                                                                  1,5 - diene   48.7                                                            ______________________________________                                         .sup.a P.sub.H .sbsb.2  = 50 mm                                          

Ruthenium acetate and its adducts with triphenyl phosphine and pyridinemay be prepared as described in Example 10.

EXAMPLE 4

Molybdenum system

Activity of protonated Mo₂ (COOCH₃)₄ in the hydrogenation of hex-1-enewas as follows:

    [Mo] = 0.015 M

    [Hex-1-ene] = 1 M P'.sub.H.sbsb.2 = 40 cm Reaction temperature 35°

    Rate = 0.32 ml/min.

EXAMPLE 5

Hydroformylation

Solutions with Rh:PPH₃ of 1:2 were found to be active forhydroformylation reactions.

Rh₂ (OCOCH₃)₄ + 4HBF₄ + 4PPh₃ in methanol (corresponding to 5 mM metalconcentration) containing substrate hex-1-ene (1M) was treated with CO +H₂ (1:1) at 35°C and either 45 cm or 1 atm pressure. After 15 hours theformation of heptaldehydes was confirmed by g.l.c. The rate wasincreased at higher pressures and temperatures.

EXAMPLE 6

Acetic Acid synthesis

A 1:2 ratio of Rh:PPh₃ is also effective for the carbonylation ofmethanol to acetic acid and methyl acetate,

Rh₂ (OCOCH₃)₄ + 4HBF₄ + 4PPh₃ in methanol (ca. 2.5 mM metalconcentration was treated with CO at 100°/50 atm. pressure in presenceof a trace of methyl iodine. The formation of acetic acid was detectedby g.l.c. Using 5 ml. of a 0.02 M Rh₂ ⁴ ⁺ solution and 45 mls methanolthe reaction occurred at 100°C and 25 atm. CO.

EXAMPLE 7

Heterogeneous Catalysis

a. A 2 g sample of "Dowex" (a registered trade mark of the Dow ChemicalCompany) 50W-X8 cation exchange resin (20-50 MS mesh H form) was allowedto absorb the protonated aqueous fluoroboric acid (2M) solution ofrhodium (II) acetate (0.1 g). The now green resin was washed withmethanol and then treated with a methanol solution saturated withtriphenyl-phosphine which turned the resin red. The resin catalyst thusprepared was suspended in methanol (50 ml) and hex-1-ene (6 ml, 1M) wasadded. At 50 cm hydrogen pressure the rate of uptake at 20°C was foundto be 10 ml. min.⁻ ¹.

b. 15 ml of resin, prepared as in (a), holding Rh equivalent to a 10 mMsolution at P_(H).sbsb.2 = 45 cm, [PPh₃ ] = 5 mM, reaction temperature =25°C, gave a rate for 1 M hex-1-ene of 1 ml.min.⁻ ¹.

EXAMPLE 8

The stoichiometric protonation by HBF₄ in methanol of the benzoatecomplex Rh₂ (OCOPh)₄.2PPh₃ gives a brown-green solution which is alsocomparable in activity to the protonated acetate.

Thus, for hex-1-ene under the standard conditions of Example 2 but with[Rh] = 1.25 mM and with no added phosphine the rate of hydrogen uptakewas 4.4 ml. min⁻ ¹.

The benzoate complex itself may be obtained in a manner similar to thatof the acetate, i.e. with benzoic acid and sodium benzoate instead ofacetic acid and sodium acetate.

Bis (triphenyl phosphine) and bis (pyridine) adducts may also beobtained with the benzoate complex.

EXAMPLE 9

The table below gives data for the hydrogenation of hex-1-ene obtainedat 30°C using the Rh₂ ⁴ ⁺ /PPh₃ catalyst under a range of catalyticconditions. These results indicate the dependence of the rate ofhydrogenation as a function of [Rh,] [hex-1-ene], and H₂ pressure(P_(H).sbsb.2).

Although at the lower concentration of rhodium, hexene and H₂, theobserved rates show approximately first order dependence on each ofthese concentration variables, the rate dependencies deviate markedlyfrom linearity at the higher concentrations. This would seem to suggestthat a number of complex equilibria may be involved. As noted earlier,the ratio of Rh:PPh₃ of 1:2 is the most favourable and was usedthroughout. Rates of hydrogenation of hex-1-ene at 30°C using the Rh₂ ⁴⁺ /PPh₃ catalyst under a range of conditions.

    [Rh]  P.sub.H .sbsb.2                                                                         [Hex-1-ene] [PPh.sub.3 ]                                                                           Rate × 10.sup.4                    mM    mm        M           mM       M.sec..sup.-.sup.1                       ______________________________________                                        1.0   400       1.0         2.0      1.10                                     2.0                         4.0      2.19                                     3.0                         6.0      2.96                                     4.0                         8.0      3.48                                     2.0   400       0.5         4.0      1.23                                                     1.5                  2.98                                                     2.0                  3.38                                                     3.0                  3.58                                     2.0   150       1.0         4.0      1.62                                           200                            1.66                                           300                            1.80                                           350                            1.88                                     ______________________________________                                    

EXAMPLE 10

Protonation of Ru₂ (OCOMe)₄ Cl and Ru₂ (OCOMe)₄.

The chloroacetate is readily protonated by fluoroboric acid in methanolat 60°C under conditions similar to those used for rhodium (II) acetate.The final solution is deep blue and extremely air sensitive, turningfirst green on exposure to air and finally yellow-brown. The bluesolution is readily absorbed on to a cation exchange resin (H form) andthe eluate can be shown to contain acetic acid, as in the rhodium case.The electronic absorption spectrum of the aqueous protonated solution. λmax (E) 437 (460), 537 sh (180), is different from that of the aqueoussolution of Ru₂ (OCOMe)₄ Cl, 423 (750). The exact nature of the cationicspecies is not certain at present.

Although the blue solutions are not catalytically active under mildconditions, again like the rhodium system, the addition of a stabilisingdonor or biphyllic ligand such as triphenyl phosphine immediately givesa very active catalyst for the hydrogenation of alkenes and alkynes (seeExample 3) without causing any initial colour change. Under hydrogen theblue solution becomes a more greenish blue and, as the hydrogenation ofalkene proceeds, the solution becomes mauve.

The protonated adduct Ru₂ (OCOMe)₄.2PPh₃ in the presence of excesstriphenyl phosphine produced a catalytic species that catalysed thehydrogenation of hex-1-ene. (See example 3A).

Green ruthenium (II) acetate. Ru₂ (OCOMe)₄ is obtained by theinteraction of commercial ruthenium trichloride with acetic acid, sodiumacetate and ethanol under reflux. It is difficult to obtain the acetateentirely free of sodium acetate and solvent, but it can be readilyisolated as its green triphenyl phosphine adduct Ru₂ (OCOMe)₄.2PPh₂. Theacetate and its adduct are both diamagnetic (n.m.r.) The bis(pyridine)adducts is similarly isolatable as dark blue crystals.

A very low rate of hydrogenation was observed when using the protonatedadduct in excess triphenyl phosphine for cis-pent-2-ene and otherinternal alkenes such as cyclohexene. From this point of view theruthenium catalyst appeared to be much more selective than thecorresponding rhodium phosphine catalyst.

Selectivity was also observed between cyclic nonconjugated dienes, cycloocta - 1,5 diene being hydrogenated very rapidly in contrast to a muchslower rate for bicycle (2.2.1) hepta-2,5 diene.

What is claimed is:
 1. A process for the homogeneous liquid phase hydrogenation of an olefinically or acetylenically unsaturated hydrocarbon to produce a hydrocarbon having a lower degree of unsaturation by contact of the said starting hydrocarbon with molecular hydrogen in the presence of a catalyst solution containing a catalytically effective amount of a cation selected from the group consisting of:M₂ ^(n) ⁺ M₂ (ocor)₄ _(-n) ^(n) ⁺ M₂ (ocsr)₄ _(-n) ^(n) ⁺ and M2(scsr)₄ _(-n) ^(n) ⁺ the said solution being prepared by the addition of strong acid to a solution of a compound selected from the group consisting of M₂ (ocor)₄ m₂ (ocor)₄ l m₂ (ocor)₄ l₂ m₂ (ocsr)₄ m₂ (ocsr)₄ l m₂ (ocsr)₄ l₂ m₂ (scsr)₄ m₂ (scsr)₄ land M₂ (scsr)₄ l₂ where M is a metal selected from the group consisting of Mo, Cr, Cu, Re and metals of the platinum group; R is selected from the group consisting of methyl and phenyl; L is a ligand selected from the group consisting of H₂ O, CH₃ OH, C₂ H₅ OH, pyridine, Cl⁻ and Br^(-;) n is a positive integer from 1 to 4; (OCOR) represents a carboxylate radical; (OCSR) represents a thiocarboxylate radical, and (SCSR) represents a diethiocarboxylate radical,and the said solution including a stabilising amount of a donor ligand selected from the group consisting of pyridine, quinoline, dimethylaniline, dibutyl sulphide, dimethyl sulphoxide, triphenyl phosphine oxide, phenyl isocyanide, acetonitrile, phosphorus tri-isocyanate, phosphorus triisothiocyanate, stannous halide, germanium (II) halide and a ligand having the formula MR'₃ where M is selected from the group consisting of phosphorus, arsenic and antimony and the R' substituents, which may be the same or different, are selected from the group consisting of alkyl and aryl radicals.
 2. A process according to claim 1 in which R' is selected from the group consisting of methyl, ethyl, butyl and phenyl radicals.
 3. A process according to claim 1 in which MR₃ ' is selected from the group consisting of tributyl phosphine, triphenyl phosphine, ethyl diphenyl phosphine, dimethyl phenyl arsine, triphenyl-arsine and triphenyl stibine.
 4. A process according to claim 1 in which the metal of the platinum group is selected from the group consisting of rhodium and ruthenium.
 5. A process according to claim 4 in which a platinum group metal and triphenylphosphine are present in the approximate ratio of 1:2.
 6. A process according to claim 1 in which the strong acid is selected from the group consisting of fluoroboric acid, perchloric acid, fluorosulphuric acid, trifluoromethane sulphuric acid, sulphuric acid, hydrofluoric acid and hyrdofluoric acid in combination with a Lewis acid.
 7. A process according to claim 6 in which the Lewis acid is selected from the group consisting of a SbF₅, SiF₄ and BF₃.
 8. A process according to claim 1 in which M₂ (OCOR)₄ is selected from the group consisting of:Rh₂ (OCOCH₃)₄ Mo₂ (OCOCH₃)₄ Cr₂ (OCOCH₃)₄ Ru₂ (OCOCH₃)₄ Cu₂ (OCOCH₃)₄ Re₂ (OCOCH₃)₄ and Ir₂ (OCOCH₃)₄.
 9. A process according to claim 1 in which M₂ (OCOR)₄ L is Ru₂ (OCOCH₃)₄ Cl.
 10. A process according to claim 1 in which M₂ (OCOR)L₂ is selected from the group consisting ofRe₂ (OCOCH₃)₄ Cl₂ and Re₂ (OCOCH₃)₄ (CO)₂.
 11. A process according to claim 1 in which M₂ (OCSR)₄ is selected from the group consisting ofRh₂ (OCSCH₃)₄ Mo₂ (OCSCH₃)₄ Cr₂ (OCSCH₃)₄ Ru₂ (OCSCH₃)₄ Cu₂ (OCSCH₃)₄ Re₂ (OCSCH₃)₄ and Ir₂ (OCSCH₃)₄.
 12. A process according to claim 1 in which M₂ (OCSR)₄ L is Ru₂ (OCSCH₃)₄ Cl.
 13. A process according to claim 1 in which M₂ (OCSR)L.sub. 2 is selected from the group consisting ofRe₂ (OCSCH₃)₄ Cl₂ and Re₂ (OCSCH₃)₄ (CO)₂.
 14. A process according to claim 1 in which M₂ (SCSR)₄ is selected from the group consisting ofRh₂ (SCSCH₃)₄ Mo₂ (SCSCH₃)₄ Cr₂ (SCSCH₃)₄ Ru₂ (SCSCH₃)₄ Cu₂ (SCSCH₃)₄ Re₂ (SCSCH₃)₄ and Ir₂ (SCSCH₃)₄.
 15. A process according to claim 1 in which M₂ (SCSR)₄ L is Ru₂ (SCSCH₃)₄ Cl.
 16. A process according to claim 1 in which M₂ (SCSR)₄ L₂ is selected from the group consisting ofRe₂ (SCSR)₄ Cl₂ and Re₂ (SCSR)₄ (CO)₂.
 17. A process for the hydrogenation of an olefinically or acetylinically unsaturated hydrocarbon to produce a hydrocarbon having a lower degree of unsaturation by contact of the said starting hydrocarbon with molecular hydrogen in the presence of a heterogeneous catalyst composition consisting essentially of a cation exchange solid having exchanged on to it a cation selected from the group consisting ofM₂ ^(n) ⁺ M₂ (ocor)₄ _(-n) ^(n) ⁺ M₂ (ocsr)₄ _(-n) ^(n) ⁺ and M₂ (scsr)₄ _(-n) ^(n) ⁺ by passage through it of a solution according to claim
 1. 18. A process according to claim 17 in which the cation exchange solid is selected from the group consisting of cation exchange resins, zeolites and phosphates.
 19. A process according to claim 18 in which the cation exchange resin is in the form of porous sulphonated polystyrene resin beads.
 20. A process according to claim 18 in which the phosphate is sodium hexametaphosphate.
 21. A process according to claim 1 in which the catalyst solution is adsorbed on to activated charcoal.
 22. A process for the homogeneous liquid phase hydrogenation of an olefinically or acetylenically unsaturated hydrocarbon to produce a hydrocarbon having a lower degree of unsaturation by contact of the said starting hydrocarbon with molecular hydrogen in the presence of a catalyst solution containing a catalytically effective amount of a cation selected from the group consisting of:M₂ ^(n) ⁺ M₂ (ocor)₄ _(-n) ^(n) ⁺ M₂ (ocsr)₄ _(-n) ^(n) ⁺ and M₂ (scsr)₄ _(-n) ^(n) ⁺ the said solution being prepared by the addition of strong acid to a solution of a compound selected from the group consisting of M₂ (ocor)₄ m₂ (ocor)₄ l m₂ (ocor)₄ l₂ m₂ (ocsr)₄ m₂ (ocsr)₄ l m₂ (ocsr)₄ l₂ m₂ (scsr)₄ m₂ (scsr)₄ land M₂ (scsr)₄ l₂ where M is a metal selected from the group consisting of Mo, Cr, Cu, Re and metals of the platinum group; R is selected from the group consisting of alkyl and aryl; L is a ligand selected from the group consisting ofH₂ o, ch₃ oh, c₂ h₅ oh, co, pyridine, Cl⁻ and Br^(-;) n is a positive integer from 1 to 4; (OCOR) represents a carboxylate radical; (OCSR) represents a thiocarboxylate radical, and (SCSR) represents a dithiocarboxylate radical, andthe said solution including a stabilising amount of a donor ligand selected from the group consisting of pyridine, quinoline, dimethylaniline, tributylphosphine, triphenylphosphine, dimethylphenylarsine, triphenylarsine, triphenylstibine, dibutyl sulphide, dimethyl sulphoxide, triphenyl phosphine oxide, phenyl isocyanide, acetonitrile, phosphorus tri-isocyanate, phosphorus tri-isethiocyanate, stannous halide and germanium (II) halide. 